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Midbrain
- 1. Midbrain Visual & auditoryprocessing and reflexes Fine-tuning of voluntary movements
- 2. Midbrain • Shortest partof brain stem – 2 cm in length • Connects – Pons (post. Cranial fossa) & Diencephalon (mid. cranial fossa) – Through tentorim cerebelli
- 3. External features • Surfaces –Ventral – Dorsal • Ends – Superior (rostral) – Inferior (caudal)
- 4. Midbrain – Ventralsurface • Features – Peduncles – Interpeduncular fossa – Emerging structure • 3rd cranial nerve – On medial aspect of peduncle • 4th cranial nerve – On lateral aspect of peduncle – Only nerve emerging from dorsal aspect of brain stem
- 5. Midbrain – Ventralsurface • Crossing structures of peduncle anteriorly – Optic tract – Posterior cerebral artery • Terminal branch of basilar – Superior cerebellar artery • Branch of basilar 3rd and 4th cranial nerves are lying between the Posterior cerebral and superior cerebellar arteries
- 6. Dorsal surface- External Features •Has 4 colliculi (corpora quadrigemina) – 2 superior – 2 inferior • Separated by – Cruciform sulcus • Vertical limb ends superiorly in – Pineal body (part of epithalamus) • Vertical limb ends inferiorly in – Frenulum veli (median elevation on superior medullary velum) • Trochlear nerve emerges below the inferior colliculus
- 7. Lateral aspect ofMidbrain • Superior brachium – Passes from • Superior colliculus – To • Lateral geniculate body • Inferior brachium – Passes from • Inferior colliculus – To • Medial geniculate body
- 8. Cerebral aqueduct • Cavityof Midbrain • Connects – III ventricle • Above – IV ventricle • Below • Acts an important landmark – To divide midbrain • Into subdivisions
- 9. Internal structure -Midbrain • Mid- brain is divided by – A line drawn through cerebral aqueduct – Dorsal to the line • Tectum – Ventral to the line • Cerebral Peduncle
- 10. Internal structure -Midbrain • Cerebral peduncle part – Has a pigmented area • Rich in melanin • Known as substantia nigra • Wider medially narrow laterally • Horizontally placed • Helped to divide peduncle into 3 areas – Tegmentum (posteriorly) – Cruscerebri (anteriorly)
- 11. Transverse section ofmidbrain • Common features in inferior and superior colliculus are – Crus cerebri (or basis pedunculi) – Substantia nigra
- 12. • Pigmented layerof gray matter – Present in midbrain – Lies between pons and subthalamus – Part of extrapyramidal system – Contains nerve cells with melanin pigments – Involves in dopamine synthesis • 2 parts – Dorsal compact part (smooth) – Ventral reticular parts (spiked) Degeneration of Subtantia nigra results Parkinson’s Disease Substantia nigra
- 13. Main connections ofsubstantia nigra • Efferent fibres – Mainly to striatum • Which is caudate and lentiform nucleus – Constitutes nigrostriatal pathway • Rich in dopamine • Control of muscle tone • Prevents tremor & other involuntary movements by • Inhibiting Globas pallidus & caudate nucleus
- 14. CS of Midbrain Cruscerebri – Lies anterior to substantia nigra – Contains descending tracts – Medial 1/5 • Fronto pontine fibres – Middle 3/5 • Corticospinal & cortico-nuclear fibres – Lateral 1/5 • Parieto-pontine • Occipito-pontine fibres • Temporo-pontine • Above continuous with corona radiata & below with longitudinal fibres of basilar part of pons
- 15. • White matter •Cortico-ponto-cerebellar fibers – Synapse with pontine nuclei – Reaches cerebellum • Through middle cerebellar peduncle • Corticonuclear fibers – To motor nuclei of cranial nerve • Corticospinal fibers – Form the pyramids CS of Midbrain Crus cerebri
- 16. Internal features –Inferior collicular level Tectal part - Grey matter • Nucleus of Inferior colliculus • Reflex center for auditory stimuli
- 17. Internal features –Tectalpart Inferior collicular level • Inferior colliculus – Act as relay station for auditory pathway – Reflex centre for response to auditory stimuli • Afferent fibres – Lateral lemniscus – Cortical fibres • Efferent fibres – Medial geniculate body • By inferior brachium • Connections for co-ordination – Efferent to • Superior colliculi • Motor nuclei of cranial nerves – Tecto bulbar • Spinal motor neurons – Tecto spinal » Seen in middle part of tegmentum
- 18. Internal features –Tegmental & tectal part Lower midbrain • Trapezoid body – Lies in lower part of pons – Decussation of the fibres from cochlear nuclei – Ascend as lateral lemniscus • Lateral lemniscus – Seen • Upper pons • Lower midbrain • End in inferior colliculus
- 19. Internal features –Tegmental part Inferior colliculus level • Contains – Grey matter • Cranial nerve Nuclei – White matter • Ascending • Descending • Crossing
- 20. Internal features –Inferior collicular level Tegmentum • Grey matter – Cranial nerve nuclei • Trochlear nucleus – Lies in ventral part of central grey matter • Mesencephalic nucleus of trigeminal – Lies in lateral part of central grey matter – Proprioceptive fibres from muscles of mastication
- 21. Internal features Inferior collicularlevel Tegmentum • Ascending tracts • Has 4 lemnisci – Lateral lemniscus conveys • Auditory sensation to inferior colliculus from two ears, mainly the opposite ear – Spinal lemniscus conveys • Pain, temperature, touch and pressure sensations from opposite side of body – Trigeminal lemniscus conveys • Sensations from opposite side of face – Medial lemniscus conveys • Discriminative touch and vibration sense from opposite side of body
- 22. Internal features –Tegmental part Lower midbrain • Lateral lemniscus – Seen • Upper pons • Lower midbrain
- 23. Anterolateral system • Spinallemniscus – Carry contralateral • Anteior spinothalamic – Crude touch • Lateral spinothalamic – Pain & temperature – Can be seen • Medulla • Pons • Midbrain
- 24. • First orderneuron – Located in • Trigeminal ganglion • Second order neuron – Located in • Spinal nucleus – (Pain & temperature) • Main pontine nucleus – (touch & pressure) • Trigeminal lemniscus – Fibres from second order neuron – Cross opposite side – Form trigeminal lemniscus • Third order neuron – Lies in thalamus Trigeminal lemniscus
- 25. Dorsal system • Mediallemniscus – Carry dorsal column modalities • From contralateral side – Can be seen • Upper medulla • Pons • Midbrain
- 26. CS of Midbrain Inferiorcollicular level • Descending tracts • Present in peripheral part of tegmentum – Lateral lemniscus – Spinal lemniscus – Trigeminal lemniscus – Medial lemniscus
- 27. Internal features –Tegmental part Lower midbrain • Decussating fibres – Decussation of superior cerebellar peduncle • Mainly dentate rubral fibres – Fibres arising from • Dentate nucleus • Passing through superior cerebellar peduncle • Main destination is Red nucleus • Those fibres decussate here – In the midline – At anterior part of Tegmentum
- 28. Internal features –Tegmental part Inferior collicular level • White matter – Fibres interconnecting cranial nerve nuclei • Medial longitudinal fasciculus – Descending tracts • Tectospinal • Rubrospinal – Lies ventral to decussation of superior cerebellar peduncle
- 29. Medial Longitudinal Fasciculus •Formed of – Descending & ascending fibers • Has two components – Ascending component • Establishes connections with the nuclei of – Occulomotor, Trochlear & Abducent nerves (motor nuclei for extraoccular muscles) for coordination of head & eye movements – Descending component • Extends into the spinal cord as the medial vestibulospinal tract
- 30. Rubrospinal Tract • Origin –From red nucleus – Located in midbrain • Termination – Lateral column of spinal cord • Seen at – Lower midbrain – Pons – Medulla
- 31. Tectospinal Tract • Origin –Superior colliculus of midbrain • Termination – Anterior Column • Function – Motor function of the Skeletal muscles of the head and eyes in response to visual stimuli
- 32. Internal features –Tegmental part Inferior collicular level • White matter – Fibres interconnecting cranial nerve nuclei • Medial longitudinal fasciculus – Descending tracts • Tectospinal • Rubrospinal – Lies ventral to decussation of superior cerebellar peduncle
- 33. Internal features –Tegmental part Superior colliculus level • Contains – Grey matter • Cranial nerve Nuclei • Red nucleus – White matter • Ascending • Descending • Crossing
- 34. Internal features –Tegmental part Superior colliculus level • Grey matter – Cranial nerve • III nerve nuclei – Nerve emerging through anterior aspect – Passing through Red nucleus – Supplies all extraocular muscles » Except • Lateral rectus • Superior obliquus • Edinger westphal nucleus (dorsal part of oculomotor complex) – Fibres passing along with III N – Supplies intra ocular muscles » Sphincter pupillae » Ciliaris • Mesencephalic nucleus of V – Lies in lateral part of central grey matter – Proprioceptive fibres from muscles of mastication
- 35. Red Nucleus • Ovoidmass of grey matter • Involved in motor control • Pink in colour – in fresh state • Has multipolar neurons • Situation – In tegmentum – Dorsal to medial part of substantia nigra
- 36. Red nucleus -connections • Afferents – Corticorubral tract: • from motor and premotor areas of cerebral cortex – Dentatorubral tract: • from opposite dentate nucleus of cerebellum • Forms decussation in lower midbrain
- 37. Red nucleus -connections • Efferent • Cross in ventral tegmental decussation • Forms Rubrospinal tract • Can be seen in lower midbrain & lower brainstem – Rubrothalamic tract • To thalamus (VA & VL nuclei) • Lesion – results in signs of cerebellar damage • contralateral tremor and ataxia
- 38. Internal features –Tegmental part Superior colliculus level White matter • In midline – Medial longitudinal fasciculus – Decussating fibres • Dorsal tegmental decussation – Fibres arising from superior colliculus forms – Continues as tecto spinal & tectobulbar tracts • Ventral tegmental decussation – Fibres arising from red nucleus forms – Then continues as rubrospinal tract
- 39. Internal features –superior collicular level Tectal part - Grey matter • Superior colliculus – Part of visual system – Optic reflex center • Changing the position of eyes & head in response to moving objects • Afferents are – From retina • Through superior brachium (visual) – From spinal cord • Through Spinotectal (touch sense) – From inferior colliculus • Auditory impulses – Corticotectal fibres • From – Visual cortex of occipital lobe – Frontal eye field of frontal lobe
- 40. Internal features –superior collicular level Tectal part - Grey matter Superior colliculus • Efferent fibres – Tectospinal – Tecto bulbar • Forms dorsal tegmental decussation
- 41. Internal features –superior collicular level Tectal part - Grey matter • Pretectal nucleus – Response for pupillary light reflex • Situation – Close to superior colliculus – At junction of midbrain & diencephalon • Afferents – Retina, superior colliculus, visual cortex • Efferent – Edingerwestphal
- 42. Arterial supply • Basilararteries • Branches of basilar – Posterior cerebral – Superior cerebellar • Posterior communicating • Anterior choroidal
- 43. Weber’s syndrome • Lesionin ventral part of midbrain – Mainly due to occlusion of posterior cerebral artery • Involves oculomotor nerve & basis pedunculi – Upper motor neuron paralaysis of opposite side – Paralysis of all muscles supplied by oculomotor • Lateral squint
- 44. Benedikt Syndrome • Necrosisinvolves medial lemniscus, spinal lemniscus and red nucleus – Ipsilateral lateral squint • Due to oculomotor involvement – Contralateral pain & temperature loss • Due to spinal lemniscus involvement